HOMO band structure and anisotropic effective hole mass in thin crystalline pentacene films

The band dispersion of the two highest occupied molecular orbital (HOMO)-derived bands in thin crystalline pentacene films grown on Bi(001) was determined by photoemission spectroscopy. Compared to first-principles calculations, our data show a significantly smaller bandwidth and a much larger band separation, indicating that the molecular interactions are weaker than predicted by theory---a direct contradiction to previous reports by H. Kakuta et al. [Phys. Rev. Lett. 98, 247601 (2007)]. The effective hole mass m^ at M̄ is found to be anisotropic and larger than theoretically predicted. Comparison of m^ to field effect mobility measurements shows that the band structure has a strong influence on the mobility even at room temperature.